1. Field of the Invention
The present invention generally relates to an optical stylus configured as a pointer for use in an optical digitizer used for inputting in a computer a coordinate indicated by the pointer or another pointing object such as a finger, a stylus or a pointing stick (hereafter, generically referred to as a pointer) disposed on a coordinate plane by optically detecting the position of the pointer with an image sensor from a periphery of the coordinate plane. More particularly, the present invention relates to an optical digitizer suitable for constructing a pen computing system in combination with a large-sized flat display panel such as a plasma display device or a liquid crystal display device such that a screen of the flat display panel is superposed with the coordinate plane of the optical digitizer. The present invention also relates to a display apparatus provided with such an optical digitizer.
2. Description of Related Art
Recently, a large-sized plasma display panel (PDP) having a diagonal length is as large as 40 inches or more has been developed and is available for practical utilization. As for a liquid crystal display (LCD), one having a screen of the class of 40 inches has been tentatively fabricated by connecting a plurality of smaller panels together. Such large-sized display devices find convenient applications in the making of presentations in a conference room or the like by serving as a monitor screen of a personal computer, for example. If a pointing operation or a marking operation on a personal computer is performed by touching the screen with a finger directly or with a stylus rather than by operating a pointing device known as a mouse, the audience before the presentation can observe both the presenter and the screen, thereby having the sense of a presentation made by use of a blackboard for more effective presentation. Therefore, display apparatuses having the output screen unitized also as the input coordinate plane have been developed by combining a display panel, a digitizer, and a touch-sensitive panel.
Conventionally, a so-called stereo method is known as a digitizing method considered comparatively easy to combine with a large-size display, in which two television cameras are used to pick up a light point of a stylus to obtain the position thereof. As shown in FIG. 24, in the stereo method, a coordinate plane 1 is arranged thereon with a stylus 2 which can be operated manually. The stylus 2 is attached at tip thereof with a light-emitting member 24. It should be noted that the coordinate plane 1 is superimposed on a large-sized display panel such as a PDP or LCD. Around the coordinate plane 1, TV cameras 12L and 12R are arranged separately on the left and right sides, respectively. The TV cameras 12L and 12R pick up the light point of the stylus 2, and input the picked up light point into a coordinate computing processor 19 as a video signal. The coordinate computing processor 19 processes the image of the stylus 2 to compute positional information (or positional coordinate), and sends the computed positional information to a personal computer 5. Based on the input positional information, the personal computer 5 generates an image signal, and sends the same to a display panel 6. Based on the received image signal, the display panel 6 displays the positional information of the stylus 2, thereby implementing a real-time pointing operation. It should be noted that the positional coordinate of the stylus 2 can be computed based on triangulation.
Referring to FIG. 25, a side view of the conventional display apparatus shown in FIG. 24 is illustrated. The output screen of the display panel 6 made of a large-sized PDP serves also as the input coordinate plane 1. The stylus 2 is operated on the coordinate plane 1. The stylus 2 has attached at a tip thereof a light-emitting member 24 such as a light-emitting diode (LED). The two TV cameras 12L and 12R pick up the light projected or radiated from the light-emitting member 24. FIGS. 24 and 25 consequently show a typical constitution of the conventional stereo method.
However, the conventional digitizers using TV cameras such as described above are too sensitive to extraneous noise caused by lights such as indoor illumination light and sunlight entered through a room window, thereby causing operation errors. Further, the conventional digitizers, when combined with a display panel, pick up the light radiated from the screen, causing operation errors. The PDP is a display of self light-emitting type and therefore emits a considerable amount of light. As for the LCD of the transmitting type using a back light souce, light is radiated from the back plane through the screen at a considerable intensity. Especially, if the pointer is of a passive type that indirectly projects a light by reflecting an extraneous light, the light quantity projected from the pointer is smaller than that of an active type of the pointer having a light-emitting member and directly projecting a light, so that the detection of the light point is seriously affected by the extraneous light, often resulting in operation errors. Still further, because the light point on the coordinate plane is picked up by the TV cameras from the periphery of the coordinate plane, the TV cameras must be arranged around the display panel. This arrangement imposes many restrictions to the installation due to the view field and contour requirements of the TV cameras, preventing a compact installation from being realized. Yet further, positioning of the TV cameras relative to the coordinate plane is cumbersome and difficult, thereby hampering ease of use of the conventional optical digitizing systems.
It is therefore an object of the present invention to provide an optical digitizer capable of operating with stability without being affected by extraneous light including light radiated from the display panel of the digitizer. It is another object of the present invention to provide an optical digitizer capable of compact installation by removing the restrictions in mounting a detecting unit for detecting the light point of a pointer. It is still another object of the present invention to provide an optical digitizer capable of identifying a plurality of different pointers by detecting colors of pointers and processing simultaneous inputs from the plurality of different pointers. It is yet another object of the present invention to provide an optical digitizer capable of efficiently processing additional information such as writing pressure of the pointer against a coordinate plane in addition to the positional information of the pointer. It is a separate object of the present invention to provide a display apparatus for suitable use in a conference support system with the optical digitizer combined with a large-sized display panel. It is a different object of the present invention to provide an optical stylus best suited to the inventive optical digitizer.
The inventive optical digitizer is constructed for determining a position of a pointing object projecting a light and being disposed on a coordinate plane. In the inventive optical digitizer, detector means is disposed on a periphery of the coordinate plane and has a field of view covering the coordinate plane for receiving the light projected from the pointing object and for converting the received light into an electric signal. Processor means is provided for processing the electric signal fed from the detector means to compute coordinate representing the position of the pointing object. Collimator means is disposed to limit the view field of the detector means below a predetermined height relative to the coordinate plane such that through the limited view field the detector means can receive only a parallel component of the light which is projected from the pointing object substantially parallel to the coordinate plane. Shield means is disposed to enclose the periphery of the coordinate plane to block a noise light other than the projected light from entering into the limited view field of the detector means.
Preferably, the detector means comprises a pair of linear image sensors for receiving the projected light at different directions to produce electric signals representing a pair of one-dimensional images of the pointing object, so that the processor means processes the one-dimensional images to compute two-dimensional coordinate of the position of the pointing object.
Preferably, the collimator means comprises a collimator lens for converging only the parallel component of the projected light onto a receiving surface of the detector means. Specifically, the collimator lens has a flat bottom face, a flat top face and a curved lens face between the flat bottom face and the flat top face so that an optical axis of the collimator lens aligns parallel to the coordinate plane when the flat bottom face of the collimator lens is placed in contact with the coordinate plane. In such a case, the optical digitizer includes optical means having at least one of a reflector and a refractor disposed in an optical path between the collimator lens mounted on the coordinate plane and the detector means mounted above the coordinate plane for directing the light collected by the collimator lens to the detector means. Alternatively, the collimator lens has an optical axis vertical to the coordinate plane, and reflector means is disposed on the coordinate plane for reflecting the parallel component of the projected light vertically to the collimator lens.
Preferably, the inventive optical digitizer further comprises a light source for providing an illumination light over the coordinate plane, so that the detector means receives the light which is passively projected from the pointing object by reflection of the illumination light. Specifically, the light source intermittently turns on and off to provide a flashing illumination light, and the processor means processes the electric signal which is fed from the detector means in synchronization with the flashing illumination light so as to compute the position of the pointing object illuminated by the light source. Further, the detector means comprises an image sensor composed of an accumulator for accumulating electric charge generated by the received light so as to convert the received light into the electric signal, and a shutter gate which switches between an open state and a closed state in synchronization with the flashing illumination light so as to control accumulation of the electric charge in the accumulator.
Preferably, the light source intermittently turns on and off to provide the flashing illumination light while cyclically changing a color of the flashing illumination light. The detector means receives the light reflected by the pointing object having a particular surface color so that the electric signal cyclically varies in dependence on the particular surface color of the pointing object. The processor means processes the electric signal so as to discriminate the particular surface color of the pointing object as well as to compute the position of the pointing object.
Preferably, the light source provides an illumination light having a first wavelength. The detector means has an optical filter for selectively receiving the light which is projected from a fluorescent surface of the pointing object illuminated by the light source and which has a second wavelength different than the first wavelength. Specifically, the light source provides an illumination light having a first wavelength in an ultraviolet range, and the detector means has an optical filter for selectively receiving the light having a second wavelength in a visible range.
Preferably, the detector means comprises a color image sensor for receiving the projected light specific to color information assigned to the pointing object and for converting the received light into a corresponding electric signal. The processor means processes the electric signal so as to discriminate the color information of the pointing object as well as to compute the position of the pointing object.
The inventive stylus has a point light movable along a coordinate plane according to drawing operation and being used as an input for an optical digitizer which converts the point light into an electric signal to compute coordinate of a position of the point light. The optical stylus is comprised of a holder portion manipulated to perform the drawing operation, and a tip portion protruding from the holder portion and forming the point light. The tip portion is composed of a light emitting member for emitting a light and a light guide member for encapsulating the light emitting member. The light guide member is composed of a transparent material shaped into a tube having a closed tip end, an open end, an outer face and an inner face. The light emitting member is mounted in the open end of the tube. At least one of the outer face and the inner face can scatter the light emitted from the light emitting member.
Expediently, The inventive optical stylus is comprised of a holder portion manipulated to perform the drawing operation and incidental operation associated with the drawing operations, and a tip portion protruding from the holder portion and having a light emitting member for emitting a light to form the point light. The holder portion includes modulation means for controlling the light emitting member in response to the incidental operation to change a color tone of the light emitted from the light emitting member, so that the optical stylus can input information of the incidental operation into the optical digitizer in addition to information of the drawing operation.
Expediently, the inventive optical stylus is comprised of a holder portion manipulated to perform the drawing operation with variation of pen pressure, and a tip portion protruding from the holder portion and having a light reflecting member for reflecting an illumination light to form the light spot. The light reflecting member comprises a slider section having a first color and sliding up and down in response to the pen pressure, and a cover section having a second color and covering the slider section, such that a ratio of the first color and the second color of the light spot changes according to the pen pressure so that the optical stylus can input information of the pen pressure into the optical digitizer in addition to the position of the optical stylus.
The inventive display apparatus is constructed for determining a position of a pointing object projecting a light and being disposed on a coordinate plane and for coincidentally displaying the position of the pointing object on the same coordinate plane. In the inventive display apparatus, detector means is disposed on a periphery of the coordinate plane and has a view field covering the coordinate plane for receiving the light projected from the pointing object and for converting the received light into an electric signal. Processor means is provided for processing the electric signal fed from the detector means to compute coordinate representing the position of the pointing object. Collimator means is disposed to limit a vertical width of the view field of the detector means below a predetermined height relative to the coordinate plane such that through the limited view field the detector means can receive only a parallel component of the light which is projected from the pointing object substantially in parallel to the coordinate plane. Shield means is disposed to enclose the periphery of the coordinate plane and has a vertical width sufficient to block a noise light other than the projected light from entering into the limited view field of the detector means. A display panel is mounted to define a screen in superposed relation with respect to the coordinate plane. Output means is provided for displaying the position of the pointing object on the screen according to the computed coordinate.
According to the present invention, the novel optical digitizer is hardly affected by the extraneous lights including the display light radiated from the display panel. Further, the novel optical digitizer realizes compact installation by reducing the restriction of mounting the detector on the coordinate plane. Still further, the novel optical digitizer is capable of detecting the color tones of pointers, thereby recognizing a plurality of different pointers and enabling simultaneous inputs by the plurality of pointers. In addition, the novel optical digitizer is capable of efficiently transmitting additional information such as a stylus pressure applied to the coordinate plane.